Such a marker light is known from GB-A-966-357, wherein the light from a lower, non-directive light source strikes, on the one hand, two part-cylindrical collecting lenses each positioned adjacent to a saw-tooth surface, these lenses serving to focus the light into a respective light bundle with parallel rays, and on the other hand, somewhat curved reflector surfaces, located at the bottom adjacent to the side walls of the casing, these reflector surfaces serving to reflect the light toward the saw-tooth surfaces of the cover plate. With this arrangement, it is difficult to prevent a large portion of the light from striking the saw-tooth surfaces at an oblique angle with an accompanying total reflection, absorption and heat development in the cover plate. This is also due to the fact that each collecting lense co-operates with no more than two saw-tooth surfaces and that the light source has a large radial extension in relation to its distance from the collecting lenses and the reflector surfaces. Consequently, this marker light provides a relatively low light efficiency and, if the power of the light source is increased, the heat development will be too high.
A similar marker light is known from DK-C-113912, wherein a lower, point-like source emits non-directive light, which hits an upper, transparent cover plate having an upper planar surface and an incident surface, which has the shape of a toroid and which is discontinued by two diametrically opposed collecting lenses or planar cylinder lenses, the latter collecting the light into two light beams emitted from the upper surface of the cover plate in opposite directions. Even in this structure, the heat development will be strong, and it is therefore hardly useful in practical applications, since the required light intensity cannot be achieved.
Other examples of previously known marker lights of the flush-mounted type, although emitting light in only one main direction, are given in EP-B1-22106 and US-A-3 096 024, these two lights including a transparent cover plate having a planar upper surface and a saw-tooth lower surface. The light source is obliquely positioned, in this case so that its light bundle strikes one of the surfaces of each saw-tooth at a substantially right angle. In principle, these known lights can be supplemented by a second light source, inclined in an opposite direction, so that two oppositely directed light beams are obtained. However, such an arrangement is disadvantageous because of the complications involved in arranging two separate light sources, and because of the increased heat development caused by another light source.